A CTP system accepts input jobs/pages written in a page description language, for example, Postscript. The jobs are sent through a raster image processor to a platemaker for exposure. The platemaker engine images the raster data on a plate, which is later mounted on the press, inked and made ready for printing.
The inclusion of a CTP system in a printing operation suggests a greater extent of automation that can be achieved. A full CTP process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate.
Also included in the automation of a CTP system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker engine and it is desirable to reduce the amount of operator handling involved. Unexposed plates are normally supplied in packages of 25 to 100 plates, with interleaf paper-sheets between the plates for protecting the emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates needs to be loaded into a supply area of a platemaker in a manner that will keep the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheets from the stack.
U.S. Pat. No. 5,992,324 to Rombult et at describes an automatic plate loading system, including a plate handler, in which plates are stored horizontally in equal-sized stacks and a slip-sheet removal mechanism. When the stack containing plates of the required size has been positioned in an access position inside the plate handler, a feeding mechanism picks the topmost plate and transports it to the imaging area. Air flow is then activated to peel off an edge of the slip-sheet, followed by gripping the peeled-off edge by mechanical “fingers” and lowering the cassette to further separate the slip-sheet from the plate above. The slip-sheet is then sucked by suction-cups, to separate it from the plate underneath and is rotatably driven out of the cassette and released.
The Lotem CTP machine, produced and sold by Creo Inc., Canada, also includes a horizontal plate-storage in cassettes, wherein the cassettes move vertically and the active cassette slides out of the storage area and into a plate-picking position within the imaging unit, where a picker picks the topmost plate and subsequently the slip-sheet lying underneath the picked plate.
These loading systems, though efficient, require extensive use of floor space for accommodating the plate storage area, the imaging system and the transport space for moving the picked plate from the storage area to the imaging unit. The design of these systems requires additional floor space for supplying new plates to the plate storage area, on one of the sides of the plate storage area different from the picking side, to enable smooth operation of the loading/imaging system while refilling plates into empty cassettes.
U.S. Pat. No. 6,341,932 to Otsuji discloses a plate loading mechanism comprising a plurality of cassettes stacked vertically; a slide mechanism for horizontally moving one of the cassettes; a lift mechanism for supporting and vertically moving the one of the cassettes horizontally moved by the slide mechanism, to a plate feed position for feeding plates to the image recording apparatus; and a transport mechanism for transporting the plates to the image recording apparatus from the one of the cassettes moved to the plate feeding position by the lift mechanism. This plate feeding apparatus is constructed to horizontally slide and then vertically move a cassette to place the cassette in the plate feed position for feeding plates to the image recording apparatus. The apparatus overcomes the first problem of the devices described above, namely the need to move vertically a number of plate-filled cassettes, yet, although proclaiming to be compact, fails to overcome the second problem of excessive floor space.
U.S. patent application Ser. No. 10/354,567 provides an improved plate loader that additionally reduces the required floor-space.
FIG. 1 is a schematic drawing of the CTP device of the prior-art. A cassette 15 is loaded, either manually or automatically, in the direction of arrow 18, onto table 14. A plate, picked from cassette 15, is transported by any means known in the art, such as vacuum, towards external drum 10, either directly or via intermediate station 12. Intermediate station 12 may serve for aligning and/or punching the plate prior to loading it onto the external drum 10 for imaging. After imaging, the plate is unloaded in the direction of arrow 20, preferably towards an in-line processor (not shown). The slip-sheets separating the plates are removed by any slip-sheet removal mechanism known in the art (not shown), and discarded into bin 16.
FIG. 2 shows the same schematic CTP layout as in FIG. 1, with an additional Multi-Cassette Unit (MCU) 22. Cassette 15 is transported from MCU 22 to table 14. MCU 22 comprises a number of cassettes 24, stored horizontally one on top of the other, each cassette preferably holding plates of a single size (26, 28). Each cassette preferably holds a plate-size different from the other cassettes. When new plates have to be filled in a cassette, the empty cassette is drawn out of the MCU 22 in the direction of arrow 30, plates filled manually, and cassette pushed back into its vertical position in the MCU.
All these prior-art plate-loading systems comprise configurations of a single plate loader serving a single CTP imager.
Luscher. AG of Switzerland provides the Xpose! automatic CTP system, using one plate loader to serve two internal drum plotters. A plate loader is positioned between the two plotters. A plate gets wrapped around a drum, which then moves towards one of the plotters and inserts the plate therein. The drum is then free to repeat the loading operation for the second plotter.
When long shifts of unattended plate-imaging are required, or, alternatively, a large number of different plate sizes is required for a certain run, the operation is limited by the number of cassettes in the MCU, usually not more than five. It would be advantageous to have a larger available number of on-line cassettes to attend to these needs.